Mammalian female fertility involves a cyclic phenomenon regulated by an interplay of protein hormones (gonadotropins - luteininizing hormone (LH) follicle stimulating hormone (FHS), and prolactin), from the pituitary, and steroid hormones (estrogens and progesterone) from the ovary. The gonadotropins act in a positive manner to stimulate production of the steroids. In turn, the gonadal steroids exert control over pituitary secretion of gonadotropins, resulting in a repeating, fairly predictable release of gonadotropins and steroids, each regulating the other.
The gonodotropins, acting on the ovary via the circulatory system, are directly responsible for follicular growth and maturation and release of the ovum from the ovarian follicle. The steroids maintain the reproductive tract and provide environments suitable for fertilization in the oviduct and implantation and maintenance of the embryo in the uterus.
Once each cycle, when the ovum inside the ovarian follicle is mature, changing blood levels of steroids inform the brain, causing the release of a large amount of LH. This pre-ovulatory surge of LH initiates ovulation with release of the ovum into the oviducts, where contact with sperm results in a fertilized ovum. The ovum then passes into the uterus, implants in the uterine wall and pregnancy has occured. Selective suppression of the pre-ovulatory surge of LH results in loss of ovulation and subsequent loss of fertility since the mature ovum is not made available to the sperm.
In the case of the male, the analogous FSH is responsible for spermatogenesis while LH is responsible for production of androgens which act to regulate pituitary secretion of gonadotropins. The androgens also promote spermatogenesis, matures sperm cells, and maintain the male reproductive tract. Therefore, any interference with pituitary secretion of gonadotropins will decrease or eliminate sperm production.
To date, the majority of birth control drugs depend on the introduction of continued physiological high levels of estrogen and/or progesterone into the subject. These steroids inhibit pituitary secretion of gonadotropins with resultant loss of cyclic activity and a relatively quiescent ovary which does not produce mature ovum. Well documented side effects of present steroid birth control drugs result from the continuous high levels of steroids and the fact that steroids act throughout the body, mediating various processes. Side effects include carcinogenic properties, increased blood pressure high incidence of blood clots, etc. An endogenously occurring peptide birth control drug would, (1) not involve introducing high steroid blood levels, thus eliminating the above side effects, (2) act on the gonadotropin hormones which act only on the ovary, and indirectly cause a decrease rather than an increase of endogenous steroids, (3) involve the introduction of a naturally occurring compound, for which the body possesses the necessary metabolic pathways, and (4) stop the process of reproduction prior to fertilization, thus eliminating a religious objection to the termination of life conception.